Domain propagation arrangement

ABSTRACT

A magnetically soft overlay strip defines a multiposition shift register path in a slice of material in which single-wall domains can be moved. The strip also defines a stable location for a single-wall domain to either side thereof for each position in the register. Domains are moved along the path by consecutively offset fields operative simultaneously to both sides of the strip, thus achieving a two-state shift register.

United States Patent Copeland, III

[ Jan. 18, 1972 [54] DOMAIN PROPAGATION ARRANGEMENT 3,553,661 1/197l Hadden, Jr ..340/l74 TF Primary Examiner-Stanley M. Urynowicz, Jr.

[72] Inventor: John Alexander Copeland, III, Gillette, Attorney-R. J. Guenther and Kenneth B. Hamlin [73] Assignee: Bell Telephone Laboratories, Incorporated,

[52] US. Cl ..340/l74 TF, 340/174 SR [5 7] ABSTRACT A magnetically soft overlay strip defines a multiposition shift register path in a slice of material in which single-wall domains can be moved. The strip also defines a stable location for a single-wall domain to either side thereof for each position in the register. Domains are moved along the path by consecutively offset fields operative simultaneously to both sides of the strip,

51 ...Gllcll/14,Gllcl9/00 58 Field of Search ..340/174 TF 174 SR thus a [56] References Cited 12 Claims, 4 Drawing Figures UNITED STATES PATENTS 3,541,534 11/1970 Bobeck et a1. ..340/174 TF INPUT PULSE SOURCE CONTROL CIRCUIT UTILIZATION CIRCUIT BIAS FIELD 25 SOURCE alsasLsai PATENTED JAN 1 8 I972 BIAS FIELD 25 SOURCE L FIG.

mu mumsom ww Sa bn z CONTROL CIRCUIT FIG. .2

/Nl/E/VTOR J. A. COPELAND ZZZ ATTORNEY TM. E 0 B PM UE v S E E M D m S S a m DOMAIN PROPAGATION ARRANGEMENT FIELD OF THE INVENTION BACKGROUND OF THE INVENTION A single-wall domain is a magnetic domain encompassed, in the plane of a material in which it can be moved, by a domain wall which closes on itself to form a stable entity free to move in the plane. A typical material for such an arrangement is a rare earth orthoferrite or a garnet crystal having a preferred direction of magnetization along an axis out of the plane of movement, nominally normal to the plane. It is convenient to designate one direction along the axis (viz, the positive direction) as the direction of the magnetization of the domain, the remainder of the material having its magnetization in the negative direction. Such a convention permits a domain to be represented as an encircled plus sign in a field of negative signs or, most simply, as a circle. A single-wall domain and an arrangement for manipulating such domains are disclosed in U.S. Pat. No. 3,460,116 of A. H. Bobeck, U. F. Gianola, R. C. Sherwood, and W. Shockley, issued Aug. 5, I969.

Single-wall domains in a sheet of material are constrained to a given diameter typically by a bias field of a polarity to constrict domainsa negative polarity according to the assumed convention. Domains are moved in the sheet by a field (viz, a field gradient) which is provided in positions consecutively offset from the position occupied by a domain.

Field gradients for moving domains are provided generally by pulses applied to an array of conductor loops adjacent the surface of the material in which the domains are moved. By pulsing a succession of conductors consecutively offset from the position occupied by a domain, consecutively offset gradients are established for causing domain displacement. In practice, the conductors are interconnected serially in three sets to provide a familiar three-phase shift register operation for domain patterns. A propagation arrangement of this type is disclosed in U.S. Pat. No. 3,460,116, supra.

Generally, information is represented in a domain propagation path in binary form by having the presence of a domain at a particular position represent a one and the absence of a domain represent a zero. In such an arrangement, it is possible for a domain to shift from one position into an adjacent empty position during propagation thus causing a double error in the stored information. Further, in order to change such stored information, it is necessary to create or annihilate domains. These operations require additional circuit elements and, in addition, input currents much larger than those needed for domain propagation. Moreover, because of the mutual repulsive force exhibited by domains on one another, the minimum spacing between domains is on the order of four domain diameters in material with low coercive force.

An object of this invention is to provide a domain propagation arrangement which permits a reduction in the minimum spacing between consecutive positions and obviates circuitry for domain creation and annihilation.

BRIEF DESCRIPTION OF THE INVENTION A propagation channel for single-wall domains in accordance with this invention is defined in a sheet of material, in which such domains can be moved, by a strip of magnetically soft material adjacent the surface of the sheet and extending from an input to an output position. The strip has a thickness-to-width ratio which defines a stable location for a domain to either side of it. A pair of interleaved conductors crisscrosses the strip to define a sequence of positions each including a pair of such locations. When the conductors are pulsed in the alternative, domains move to like locations of consecutive location pairs.

In an alternative embodiment, a single conductor is employed for moving domains. Permalloy dots or recesses are utilized to offset domains moved by that conductor thus functioning as would a second conductor.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration of a domain propagation arrangement in accordance with the invention;

FIGS. 2 and 3 are schematic illustrations of a portion of the arrangement of FIG. 1 showing the magnetic condition thereof during operation; and

FIG. 4 is a cross-sectional view of the portion of the arrangement shown in FIG. 3.

DETAILED DESCRIPTION FIG. 1 shows a domain propagation arrangement including a slice or sheet 11 in which a representative channel for domain movement is defined. The channel comprises a magnetically soft strip 12 of, for example, low coercive force permalloy aligned with the axis of the channel represented by broken line 13 in FIG. 1 and shown as a closed loop, for the recirculation of information. Strip 12 is crisscrossed by electrical conductors l4 and 15 offset with respect to one another and having, illustratively, a serpentine geometry. The conductors are conveniently deposited on opposite sides of a plastic substrate and juxtaposed with sheet 11.

The repeat patterns of the conductors define consecutive positions along the channel for single-wall domains as indicated by the domains D in FIG. 1. Permalloy strip 12 defines a stable location for a domain to either side thereof for each position defined by the conductors. Thus locations below strip 12 as viewed in FIG. 1 may be taken to represent binary zero locations, whereas locations above the strip may be taken as representing binary one locations. In operation, all the binary zero locations are occupied normally by domains for recirculation about closed loop 13 as conductors 14 and 15 are pulsed in the alternative, first with positive and then negative pulses. If a binary one is required in a particular position, the domain occupying the zero location in that position is moved to the corresponding one location as shown for domain D in FIG. 2.

Movement of a domain from a zero to a one location is accomplished by an input conductor 20. Conductor 20 is connected between an input pulse source 21 of FIG. 1 and ground. When a pulse of a polarity to constrict domains is applied to conductor 20 by source 21, domain D of FIG. 2 is repelled to a one location. When a pulse of a polarity to attract domains is applied, domain D moves to the zero location, as shown in FIG. 3. Selective activation of conductor 20 introduces a pattern of domains in first and second locations for movement, by consecutively offset fields, as conductors l4 and 15 are pulsed, thus representing binary information in channel 13.

Information so formed and moved in the channel is detected at an output position indicated by an encircled X in FIG. 1. In practice, a familiar electrical probe is placed to indicate the passage of a domain in a one location at the output position. The probe may be a simple conductor loop or a Hall probe, or detection may be accomplished by optical means such as via the Faraday or Kerr effect. Such alternatives are familiar in the art and are not discussed in detail here. Any signal so generated is applied to a utilization circuit 24 of FIG. 1.

The diameter of a domain in the arrangement of FIG. 1 is maintained at a nominal value by a bias field of a polarity to constrict domains. A source of such a field is represented by block 25 in FIG. 1. Sources 21 and 25 and circuit 24 are connected to a control circuit 26 for synchronization and control. The various sources and circuits may be any such elements capable of operating in accordance with this invention.

It is important to note that a propagation channel in accordance with this invention includes a plurality of consecutive positions for domains, each of which comprises first and second stable locations laterally displaced with respect to one another thus forming a location pair for each position. The

first and second location sets in a single propagation channel, in turn, define associated binary one and binary zero channels respectively.

A variety of advantages arise from such an arrangement. Firstly, there is no need to generate or annihilate domains. Rather, binary zeros can be recirculated and merely displaced to the associated one location for representing information. Secondly, relatively little current is necessary to so displace a domain. Thirdly, since lateral movement of domains is inhibited and mutual repulsion forces along the path are counterbalanced between preceding and subsequent domains, a relatively rigid force structure is formed which militates against information loss and leads to increased packing densities. Minimum domain spacings of two domain diameters are achieved as a result.

The realization of two stable locations at each bit position depends on the thickness-to-width ratio of the permalloy strip and the ratio of width of the permalloy strip to the diameter of the domain being moved. Unless the thickness-to-width ratio is less than the ratio of the domain magnetization to the permalloy magnetization, domains occupy positions directly below the permalloy strip rather than in first or second stable positions. The reason for this is that the internal demagnetizing fields in the permalloy strip, which are proportional to the product of permalloy magnetization and thickness of the strip divided by the width of the strip, must be smaller than the external demagnetizing field of the domain over most of the volume of the strip in order to avoid an energy minimum when a domain occupies a position directly under the strip.

FIG. 4 shows a cross section through sheet 11 and conductors l4 and 15 of FIG. 1 taken along line 44 as shown in FIG. 3. The two stable positions are indicated as the 1" and the sides. The domain is shown on the 0" side with its wall under strip 12.

The lateral location of the domain is stable when the length of domain wall beneath the permalloy pattern is at a local maximum. For a single permalloy strip, there are two stable lateral positions only when the width of the strip is less than the domain diameter. The amount of force required to move a domain from zero to one" position is greatest when the strip width is about one-half the domain diameter so this width is optimum for regions of the path where only propagation takes place. A reduction in width of the strip to about 0.2 domain diameters is advantageous at output positions to increase the lateral separation between the zero and one" position. An increase to about 0.7 domain diameters in the width of the strip is advantageous at input positions to reduce the current needed to shift the lateral position of the domain.

In practice, sheet 11 can be notched (notch 30-FIG. 4) as a substitute for strip 12.

In an illustrative embodiment of this invention, domains having diameters of 100 micrometers are moved in a slice of thulium orthoferrite 50 micrometers thick, each domain having a magnetization of 0.0l weber per meter square. The propagation channel is defined by a permalloy strip having a (magnetization of 0.8 weber per meter square and a) coercive force of 300 amperes per meter (less than 4 oersteds) and a width and thickness of 50 micrometers and 50 nanometers, respectively. A bias field of 2,000 amperes per meter maintains the domain diameter and currents of about 50 milliamperes cause domain movement. Domains are spaced about 200 micrometers apart during operation. Write currents of about 40 milliamperes are employed.

What has been described is considered only illustrative of the principles of this invention. Therefore, modifications can be devised by those skilled in the art in accordance with those principles within the spirit and scope of this invention. For example, the wiring configuration for supplying drive fields as shown in FIGS. 2 and 3 is merely illustrative and alternatives may be used. My copending application, Ser. No. 50,568 filed June 29, I970, discloses one circuit suitable for this purpose. Moreover, only one-half (viz, a binary one channel) may be used to advantage in accordance with this invention.

What is claimed is: I l. A domain propagation arrangement comprising a material in which single-wall domains can be moved, and propagation means for moving a domain from an input to an output position in said materiaLsaid propagation means comprising means for providing in a sequence of positions between said input and output positions patterns of magnetic fields for moving domains from position to position in a channel therebetween, and means for defining in each of said positions first and second stable locations for a domain, said last-mentioned means being of a geometry to require movement of domains to like locations of consecutive positions of said channel in response to said magnetic fields.

2. A domain propagation arrangement in accordance with claim 1 wherein said means for defining comprises a permalloy strip extending between said input and output positions having a thickness and width to define said first and second 10- cations to either side thereof.

3. A domain propagation arrangement in accordance with claim 2 wherein each of said domains has a first magnetization and said strip has a second magnetization where the ratio of the thickness of said strip to the width thereof is less than the ratio of said first to said second magnetization.

4. A domain propagation arrangement in accordance with claim 3 wherein said permalloy strip is of a geometry such that the internal demagnetizing field therein is smaller than the demagnetizing field of a domain in said material.

5. A domain propagation arrangement in accordance with claim 2 wherein the width of said strip at said output position is smaller than said width of said strip between said input and output position.

6. A domain propagation arrangement in accordance with claim 2 wherein the width of said strip at said input position is larger than said width of said strip between said input and output position.

7. A domain propagation arrangement in accordance with claim 5 wherein the width of said strip at said input position is larger than said width of said strip between said input and output positions.

8. A domain propagation arrangement in accordance with claim 7 including means for selectively moving domains between first and second stable locations at said input position, and means for selectively detecting domains at said output position.

9. A domain propagation arrangement in accordance with claim 1 wherein said means for defining comprises a groove in said material extending between said input and output positions.

10. A domain propagation arrangement in accordance with claim 2 wherein the width of said strip is less than the diameter of a domain in said material.

11. A domain propagation arrangement in accordance with claim 2 wherein the width of said strip equals the radius of a domain in said material.

12. A domain propagation arrangement comprising a material in which single-wall domains can be moved, and means for moving a domain from an input to an output position in said material, said means comprising a strip of magnetically soft material overlying said material and extending between said input and output positions, said strip having a thickness-to-width ratio for defining first and second stable locations to first and second sides thereof, and means for provid ing like magnetic fields in a sequence of positions along said strip for simultaneously moving domains in said first or second stable locations of said positions to like locations of consecutive positions. 

1. A domain propagation arrangement comprising a material in which single-wall domains can be moved, and propagation means for moving a domain from an input to an output position in said material, said propagation means comprising means for providing in a sequence of positions between said input and output positions patterns of magnetic fields for moving domains from position to position in a channel therebetween, and means for defining in each of said positions first and second stable locations for a domain, said last-mentioned means being of a geometry to require movement of domains to like locations of consecutive positions of said channel in response to said magnetic fields.
 2. A domain propagation arrangement in accordance with claim 1 wherein said means for defining comprises a permalloy strip extending between said input and output positions having a thickness and width to define said first and second locations to either side thereof.
 3. A domain propagation arrangement in accordance with claim 2 wherein each of said domains has a first magnetization and said strip has a second magnetization where the ratio of the thickness of said strip to the width thereof is less than the ratio of said first to said second magnetization.
 4. A domain propagation arrangement in accordance with claim 3 wherein said permalloy strip is of a geometry such that the internal demagnetizing field therein is smaller than the demagnetizing field of a domain in said material.
 5. A domain propagation arrangement in accordance with claim 2 wherein the width of said strip at said output position is smaller than said width of said strip between said input and output position.
 6. A domain propagation arrangement in accordance with claim 2 wherein the width of said strip at said input position is larger than said width of said strip between said input and output position.
 7. A domain propagation arrangement in accordance with claim 5 wherein the width of said strip at said input position is larger than said width of said strip between said input and output positions.
 8. A domain propagation arrangement in accordance with claim 7 including means for selectively moving domains between first and second stable locations at said input position, and means for selectively detecting domains at said output position.
 9. A domain propagation arrangement in accordance with claim 1 wherein said means for defining comprises a groove in said material extending between said input and output positions.
 10. A domain propagation arrangement in accordaNce with claim 2 wherein the width of said strip is less than the diameter of a domain in said material.
 11. A domain propagation arrangement in accordance with claim 2 wherein the width of said strip equals the radius of a domain in said material.
 12. A domain propagation arrangement comprising a material in which single-wall domains can be moved, and means for moving a domain from an input to an output position in said material, said means comprising a strip of magnetically soft material overlying said material and extending between said input and output positions, said strip having a thickness-to-width ratio for defining first and second stable locations to first and second sides thereof, and means for providing like magnetic fields in a sequence of positions along said strip for simultaneously moving domains in said first or second stable locations of said positions to like locations of consecutive positions. 